Colon cancer is a malignancy in the colon. It is characterized by unregulated replication of cells creating tumors, with the possibility of some of the cells spreading to other sites (metastasis).

This article includes a discussion of studies that have assessed whether certain vitamins, minerals, herbs, or other dietary ingredients offered in dietary or herbal supplements may be beneficial in connection with the reduction of risk of developing colon cancer, or of signs and symptoms in people who have this condition.

This information is provided solely to aid consumers in discussing supplements with their healthcare providers. It is not advised, nor is this information intended to advocate, promote, or encourage self prescription of these supplements for cancer risk reduction or treatment. Furthermore, none of this information should be misconstrued to suggest that dietary or herbal supplements can or should be used in place of conventional anticancer approaches or treatments.

It should be noted that certain studies referenced below, indicating the potential usefulness of a particular dietary ingredient or dietary or herbal supplement in connection with the reduction of risk of colon cancer, are preliminary evidence only. Some studies suggest an association between high blood or dietary levels of a particular dietary ingredient with a reduced risk of developing colon cancer. Even if such an association were established, this does not mean that dietary supplements containing large amounts of the dietary ingredient will necessarily have a cancer risk reduction effect.

In Western countries, cancers of the colon and rectum account for more new cancer cases each year than any other site except the lung. Although the genetic susceptibility is low, some families have a predisposition for colon cancer that usually occurs before age 40. Inflammatory bowel disease, including both ulcerative colitis and Crohn’s disease as well as familial polyposis, are disorders that, to varying degrees, increase the risk of colon cancer.

For an herb, supported by traditional use but minimal or no scientific evidence. For a supplement, little scientific support and/or minimal health benefit.

What are the symptoms of colon cancer?

The initial symptoms of colon cancer depend on the location of the tumor. Cancer in the portion of the colon nearest the left side of the body and areas close to the rectum are the most common cause for a change in bowel habits and consistency of the stool. Cancer in this part of the colon may also cause a colicky pain that is made worse by eating. Blood mixed with the stool and bowel obstruction are other symptoms that characterize cancer at this site. Ineffectual and painful straining at stool may be a sign that the cancer is more advanced. Cancer localized to the part of the colon nearest the right side of the body may cause a generalized abdominal pain and brick red blood. It is commonly associated with iron-deficiency anemia, especially when no other cause can be identified. Cancers closer to the rectum often cause a steady gnawing pain and bright red blood coating the stool.

Dietary changes that may be helpful for colon cancer

The following dietary changes have been studied in connection with colon cancer.

AlcoholMost,1 2 3 but not all,4 preliminary reports have found an association between beer drinking (though not consumption of other forms of alcohol) and rectal cancer. Beer drinking has also been associated with an increased risk of precancerous changes in the colon.5 Nitrosamines––cancer-causing chemicals found in beer––may be partially responsible for these associations.6 Several studies have found consumption of any form of alcohol to be associated with an increased risk of rectal and colon cancers, the link between rectal cancer and beer being only slightly stronger than the association between rectal cancer and consumption of other forms of alcohol.7 8

Alcohol can indirectly damage DNA—the material that allows cells to replicate normally. Abnormal replication of cells can lead to cancer. Folic acid, a B vitamin, appears to protect against alcohol-induced DNA damage. Increasingly, researchers believe that folic acid may be able to protect against some of the colon cancer-causing effects of alcohol.9 10 Doctors recommend that people wishing to reduce their risks of colon and rectal cancers abstain from drinking alcohol.

Those who continue to drink should take folic acid supplements. In one report, women taking multivitamins (often containing 400 mcg of folic acid per day) for at least 15 years had a 75% lower risk of colon cancer compared with women not taking such supplements.11

FiberUntil recently, most studies reported that people who ate a high-fiber diet were found to be at low risk for colon cancer.12 Some researchers believed protection against colon cancer comes specifically from eating wheat bran13 14 15 as opposed to other fibers. A clear understanding of how fiber might protect against colon cancer risk remains somewhat elusive.16

Recent research has begun to cast doubt on whether fiber provides significant protection against colon cancer,17 18 suggesting instead that consumption of meat and other animal products may be the primary culprit. Despite these recent reports, however, some doctors continue to believe that, until more definitive information is available, people wishing to reduce their risk of colon cancer should consume more fiber in their diets.

Consuming a diet high in insoluble fiber is best achieved by switching from white rice to brown rice and from bakery goods made with white flour or mixed flours to 100%-whole-wheat bread, whole-rye crackers, and whole-grain pancake mixes. Refined white flour is generally listed on food packaging labels as “flour,”“enriched flour,”“unbleached flour,”“durum wheat,”“semolina,” or “white flour.” Breads containing only whole wheat are often labeled “100% whole wheat.”

TomatoesTomatoes contain lycopene—an antioxidant similar in structure to beta-carotene. Most lycopene in our diet comes from tomatoes, though traces of lycopene exist in other foods. Lycopene inhibits the proliferation of cancer cells in test-tube research.19

A review of published research found that higher intake of tomatoes or higher blood levels of lycopene correlated with protection from cancer in 57 of 72 studies. Findings in 35 of these studies were statistically significant.20 Evidence of a protective effect for tomato consumption was strongest for a variety of other cancers, but some evidence of a protective effect also appeared for colon cancer. Many doctors recommend that people who are not allergic to tomatoes increase their intake to reduce their risk of cancer.

Cruciferous vegetablesCabbage, Brussels sprouts, broccoli, and cauliflower belong to the Brassica family of vegetables, also known as “cruciferous” vegetables. In test-tube and animal studies, these foods have been associated with anticancer activity,21 possibly due to several substances found in these foods, such as indole-3-carbinol,22 glucaric acid (calcium D-glucarate),23 and sulforaphane.24 In a preliminary human study, people who eat cruciferous vegetables were reported to have lower-than-average risks for colon cancer.25

Meat and how it is cookedMost, but not all, studies26 show meat eaters have a high risk of colon cancer.27 28 29 In some colon cancer studies, the association has been limited to consumption of sausage or other processed meats.30 31

The association between cancer and consumption of meat depends in part on how well the meat is cooked. Well-done meat contains more carcinogenic material than does lightly cooked meat.32 Recent evidence from preliminary studies shows that people who eat well-done,33 fried or heavily-browned meat34 have a high risk of colon cancer.

However, not every report has found that exposure to carcinogens found in well-done meat leads to an increased risk of colon cancer.35 Some studies may have failed to find this link because they did not consider the effect of genetics. Susceptibility to the colon cancer-causing effects of well-cooked meat appears to be genetically determined.36 Therefore, only some people appear to increase their risk of colon cancer by consuming well-cooked meat. However, people are rarely tested to see if they are “rapid acetylators”—meat-eaters considered to be at high risk of colon cancer37 —except as subjects in a research experiment.

Most nutritionally oriented doctors tell people wishing to reduce their risk of colon cancers to stop eating meat, or at least significantly reduce consumption, and to limit intake to meat that is rare or medium-cooked. Removing all meat from the diet may be safest because consumption of even rare or medium-cooked meat has been associated with at least some increase in risk.38

Coffee“Secondary bile acids” are substances in the gut that may increase the risk of colon and rectal cancers. Some researchers have hypothesized that coffee drinking might reduce the risks of colon and rectal cancers by decreasing the intestinal level of these substances.39 40 An analysis of preliminary studies suggests coffee drinkers have a significantly lower risk of these cancers compared to the risk in people who do not drink coffee.41 However, only studies using the weakest methods of inquiry have found this protective effect. Due to the lack of support from studies using stronger methodology, the association between coffee drinking and protection against colon or rectal cancers remains unproven.42

Dietary fatDietary fat intake has long been regarded as an important nutritional influence on colon cancer development. Nevertheless, the association between colon cancer and total dietary fat remains inconsistent. Although there are known mechanisms by which a high dietary fat intake could promote tumor growth in the colon,43 a review of the research shows the strongest dietary association with colon cancer to be the intake of meat, not necessarily the fat content of the meat.44 See the discussion about Meat (how it is cooked), above.

SaltAssociations between salt intake and colon and rectal cancers are reported in some,45 but not all, preliminary studies.46 Doctors often do not mention salt restriction as part of a cancer-prevention diet because the only malignancy strongly associated with salt—stomach cancer—is no longer common in the United States despite our high intake of salt.

SugarPreliminary studies have reported associations between an increasing intake of sugar or sugar-containing foods and an increased risk colon cancer.47 48 Whether this association exists because sugar directly promotes cancer, or because sugar consumption is only a marker for some other dietary or lifestyle factor, remains unknown.

Lifestyle changes that may be helpful for colon cancer

The following lifestyle changes have been studied in connection with colon cancer.

Exercise and preventionMost studies show that people who exercise are at lower risk of colon cancer or precancerous changes in the colon, compared with sedentary people.49 50 51 52 Regular exercise appears to be one factor that will predictably lower the risk of colon cancer.

Obesity and riskSeveral studies suggest that obesity in men significantly increases the risk of colon cancer53 or rectal cancer,54 though some scientists believe that obesity may only be a surrogate for other risk factors such as a high-fat diet or lack of exercise.55 Although the relationship between obesity and colon cancer risk in women is less clear, some researchers have found the increased risk of colon cancer in obese women as well as men.56

Smoking and riskA history of smoking has been reported to significantly increase the risk of colon cancer in both men57 and women.58 Avoidance of tobacco is an important step in the prevention of colon cancer.

Nutritional supplements that may be helpful for colon cancerThe following nutritional supplements have been studied in connection with colon cancer.

Folic acidPeople with ulcerative colitis (UC) are at increased risk for colon cancer. Many patients with this disease take the drug sulfasalazine, which depletes folic acid.59 In a preliminary report, patients with long-standing UC who took folic acid supplements (at least 400 mcg per day) had a 62% lower incidence of colon cancer or precancerous changes in the colon, compared with those who did not supplement with folic acid.60 Although this difference was not statistically significant, the researchers recommended that people who take sulfasalazine should supplement with folic acid to potentially reduce the risk of colon cancer.61

As dietary folate increases, the risks of precancerous polyps in the colon62 and colon cancer itself decrease, according to some,63 but not all, reports.64 In one study, women who had taken folic acid supplements had a statistically significant 75% reduction in the risk of colon cancer, compared with women not taking folic acid supplements, but only when they had been supplementing with folic acid for more than 15 years.65 In another report, the association between dietary folate and protection from precancerous polyps grew much stronger when use of folic acid supplements was considered (as opposed to studying only folate intake from food).66

The protection from colon cancer associated with high intake of folate has been reported to occur more in consumers of alcohol than in nondrinkers.67 This finding fits well with evidence that folate reverses damage to DNA caused by alcohol consumption.68 Damaged DNA can lead to abnormal cellular replication—a step toward cancer.

Some nutritionally oriented doctors recommend folic acid supplementation for prevention of recurrences in patients who formerly had colon cancer but are now in complete remission. However, no research has yet explored the effect of folic acid supplementation in people who have already been diagnosed with cancer. Cancer patients taking the chemotherapy drug methotrexate must not take folic acid supplements without the direction of their oncologist.

SeleniumSelenium has been reported to have diverse anticancer actions.69 70 Selenium inhibits cancer in animals.71 Low soil levels of selenium, probably associated with low dietary intake, have been associated with increased cancer incidence in humans.72 Blood levels of selenium have been reported to be low in patients with a variety of cancers,73 74 75 76 77 78 79 80 including colon cancer.81 In preliminary reports, people with the lowest blood levels of selenium had between 3.8 and 5.8 times the risk of dying from cancer compared with those who had the highest selenium levels.82 83

The strongest evidence supporting the anticancer effects of selenium supplementation comes from a double-blind trial of 1,312 Americans with a history of skin cancer who were treated with 200 mcg of yeast-based selenium per day or placebo for 4.5 years, then followed for an additional two years.84 Although no decrease in skin cancers occurred, a dramatic 50% reduction in overall cancer deaths and a 37% reduction in total cancer incidence were observed. A statistically significant 58% decrease in cancers of the colon and rectum was reported.

Little is known about the effects of selenium in the treatment of people with existing cancer. Selenium supplementation was reported to improve immune function in colon cancer patients,85 but no long-term follow-up was done to evaluate whether these patients ultimately lived longer or fared better.

In the double-blind study cited above,86 the large reduction in cancer deaths found in such a short period of time (6.5 years) suggests that these researchers may have been successfully, though unknowingly, treating some people with undiagnosed cancer. However, this speculation has yet to be proven.

MelatoninThe hormone melatonin is available as a supplement and is believed by some researchers to have anticancer activity because of its effects on the immune system.87 In research trials, melatonin has been evaluated as a potential agent for use in connection with treatment for cancer patients—not to protect healthy people from getting cancer.

Patients with advanced colon cancer who had either not responded to chemotherapy, or who had relapsed after a response to chemotherapy, were given either no additional treatment (control group) or a combination of interleukin-2 and 40 mg of melatonin per day.88 Nine of 25 patients given melatonin plus interleukin-2 survived for a year compared with only three of 25 patients in the control group, a difference that was statistically significant.

Many other controlled trials suggest that melatonin may extend survival, disease-free survival, and/or quality of life in cancer patients.89 90 91 92 93 94 95 96 97 98 99 100 101 Most of these trials used 20 mg of melatonin taken at bedtime. Taking such a high amount of melatonin should be done only under the supervision of a doctor familiar with its use. Animal research suggests that the anticancer effects of this hormone may be reversed if melatonin is taken during the day. Therefore, melatonin should be taken only at night.

CalciumThrough a variety of mechanisms, calcium may have anticancer actions within the colon. Most,102 103 104 but not all,105 preliminary studies have found associations between taking calcium supplements and a reduced risk of colon cancer or precancerous conditions in the colon. In double-blind trials, calcium supplementation has significantly protected against precancerous changes in the colon in some,106 107 but not all, reports.108 109 While most evidence examining the ability of calcium supplementation to help prevent colon cancer appears hopeful, no research findings yet support the use of calcium supplements in people already diagnosed with colon cancer.

Vitamin EIn most,110 111 but not all, preliminary reports, people who take vitamin E supplements were found to have decreased risks of precancerous colon polyps and colon cancer, compared with those who do not take vitamin E.112 Although a double-blind study of male smokers reported that those receiving low amounts of vitamin E (equivalent to approximately 50 IU per day) had a higher incidence of precancerous colon polyps than those assigned to placebo,113 the same trial found a trend toward lower risk of colon cancer in the vitamin E group.114 Insufficient information exists for making recommendations regarding the use of vitamin E in connection with the prevention of colon cancer.

Vitamin CWomen, but not men, who took vitamin C supplements were reported to have a reduced risk of colon cancer, according to a preliminary report.115

Familial polyposis is a disease that usually leads to colon cancer. In a double-blind study, supplementation with 3 grams per day of vitamin C for nine months led to a reduction in the number of precancerous polyps in people with familial polyposis.116 In another controlled trial, combining vitamin C with vitamin A and vitamin E led to a dramatic reduction in the recurrence of adenomatous polyps—another precancerous condition of the colon.117 However, other trials attempting to prevent recurrence of adenomatous polyps using vitamin C alone or in combination with other vitamins have reported no therapeutic effect118 or only weak trends favoring the group given supplements.119 120

Therefore, the ability of vitamin C supplementation to reduce recurrences of precancerous polyps remains unproven. Whether long-term supplementation with vitamin C would directly help in the prevention of colon cancer has not yet been studied.

Cancer patients’ white blood cells (WBCs) have been reported to contain low levels of vitamin C when compared with WBCs of healthy people.121 In the 1970s, Linus Pauling and Ewan Cameron, a Scottish surgeon, gave 100 terminal cancer patients 10 grams of vitamin C per day (2.5 grams four times per day) and followed them until death.122 These patients lived an average of 210 days, compared with an average of 50 days for similar cancer patients who did not receive vitamin C. A follow-up report on the same patients revealed an even greater gap in survival time between the two groups.123

Mayo Clinic researchers studied the effect of vitamin C in terminal cancer patients, but unlike Pauling and Cameron, they gave about half of the patients a placebo. The Mayo Clinic findings showed that vitamin C had no therapeutic effect.124 Pauling claimed that his trial differed from the Mayo Clinic study because his patients had received much less chemotherapy. In theory, chemotherapy might inactivate vitamin C’s anticancer effects.

The Mayo Clinic therefore conducted a second controlled study, this time in colon cancer patients who had not received chemotherapy.125 Again, the Mayo Clinic reported that vitamin C was ineffective. In response, Pauling said that his patients had been given vitamin C supplements until they died. The Mayo Clinic’s colon cancer patients, in contrast, were no longer given vitamin C once their cancers progressed. Thus Pauling’s premise—that vitamin C would increase survival in terminal cancer patients if they continued to take vitamin C until they died—had not been adequately tested by the Mayo Clinic.

Pauling was also concerned that some of the colon cancer patients assigned to the placebo group may have been taking vitamin C supplements even though they had been instructed not to. The Mayo Clinic had made only limited attempts to monitor whether people in the control group were surreptitiously taking vitamin C.

In an attempt to duplicate Pauling’s findings, Japanese researchers conducted a trial with terminal cancer patients.126 As with the Pauling trial, a control group existed but was not given placebo. Patients assigned to vitamin C lived an average of 246 days compared with 43 days in those not receiving vitamin C. Thus, the Japanese research results independently confirmed the outcome of the Pauling and Cameron trial. Nonetheless, the negative reports from the controlled Mayo Clinic trials—despite criticisms of those trials—leave the issue unresolved. None of these studies investigated what effect, if any, vitamin C might have in patients with early stage colon cancer.

Vitamin DUltraviolet light from sun exposure increases the risk of skin cancers and melanoma. Nonetheless, where sun exposure is low, rates of several cancers have been reported to be high.127 128 129 An association between greater sun exposure and a reduced risk of colon cancer has appeared in some,130 but not all, studies.131

In preliminary reports, people who take vitamin D supplements have been reported to be at low risk for colon cancer, though the differences between supplement takers and others might have been due to chance.132 133 More research is needed to determine whether vitamin D supplements may be useful in connection with the prevention of colon cancer.

GlutathioneGlutathione is an antioxidant made in the body, found in some foods, and available as a supplement. Preliminary research suggests that glutathione might have anticancer activity by binding with cancer causing agents or by acting as an antioxidant.

In a preliminary report, 11 patients with late-stage or terminal colon cancer were given 800 mg of glutathione twice per day for at least three months.134 After an average of 21 weeks, three had died, four others did not improve, and four “recovered with normal diet [and] increased weight. . . . Three of the four were able to return home.” In that report, glutathione was combined with the amino acid cysteine and with anthocyans—a type of flavonoid. More research is needed to evaluate whether glutathione is an effective agent for use in connection with treatment of people with late-stage colon cancer.

Fish oilSeveral human studies have found that supplementation with omega-3 fatty acids from fish oil leads to a reduction in markers for the risk of colon cancer.135 136 137 In each case, enough fish oil was supplemented to supply several grams of omega-3 fatty acids per day, though the optimal amount remains unknown. Despite these promising reports, no trial has yet investigated whether supplementation with fish oil would actually help in the prevention of colon cancer, or be useful in connection with the treatment of people who already have been diagnosed with colon cancer.

IP-6IP-6 (also called inositol hexaphosphate, phytate, or phytic acid) is found in many foods, particularly oat and wheat bran, and unleavened (flat) bread. Until recently most IP6 research focused on interference with the absorption of minerals—a side effect of consuming IP6. More recently, however, animal studies have found that IP6 has anticancer activity,138 particularly in relation to colon cancer.139 Although these animal studies look promising, no human trials using IP6 supplements to prevent or treat cancer have yet been published.

FiberAlthough fiber is available in supplement form (such as Metamucil®) most fiber consumption results from eating food. The commonly held belief that fiber might also reduce the risk of colon cancer has recently been challenged by several trials that do not support this hypothesis. A fuller discussion of fiber and possible prevention of cancer is found in the Cancer Prevention and Diet article.

Beta-caroteneIn double-blind trials, synthetic beta-carotene supplements have had no effect on the incidence of precancerous polyps in the colon.140 141 Currently, no evidence shows that beta-carotene supplementation, either natural or synthetic, increases or reduces the risk of colon cancer.

Coenzyme Q10 (CoQ10)CoQ10 has direct effects on the immune system.142 Though high levels of CoQ10 have been found in colon and rectal cancer tissue,143 low blood levels of CoQ10 have been reported in patients with several other cancers.144 145 146

Are there any side effects or interactions with colon cancer?

Refer to the individual supplement for information about any side effects or interactions.

Herbs that may be helpful for colon cancerThe following herbs have been studied in connection with colon cancer.

Garlic (Allium sativum) and onion(Allium cepa)These two herbs belong to the group of plants known as Allium. Many other edible plants are found in this group, including leeks and chives. Preliminary studies have investigated the association between eating Allium herbs and the incidence of cancer. The most consistent data come from research focusing on the protective effects of Allium consumption against cancers of the gastrointestinal tract.147 148 149 150 151 152 Several preliminary studies have found that people who consume more Alliumvegetables appear to have a reduced risk of colon cancer153 154 and precancerous colon polyps.155

Constituents in garlic and onions prevent the conversion of nitrates (compounds found in vegetables and, to a lesser extent, in water) to cancer-causing nitrites and nitrosamines.156

Green tea and black tea (Camellia sinensis)Green and black tea have both been studied to determine whether they cause or prevent cancer. The evidence on the protective effect of either type of tea is inconsistent.157 158 159 160 161 162 163 164

A number of preliminary studies have shown an association between drinking green tea and a reduced risk of several types of cancer,165 166 167 168 including colon cancer.169 In contrast, preliminary studies found that consumers of black tea do not appear to have a reduced risk of any type of cancer.170 171 172

Other herbal therapiesNo trials have investigated the effects of the Hoxsey herbal formula, Coriolus versicolor (PSK), the Essiac formula, or most other herbal therapies specifically for the treatment of people with colon cancer.

Are there any side effects or interactions with colon cancer?

Refer to the individual herb for information about any side effects or interactions.